To be honest, considering the K-5's fairly strong AA filter, this looks like it's at the limit of the resolution for that camera. Maybe a 100% crop would tell more, but I don't see a reason here to criticise the lens.

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No amount of perceived entitlement can replace actual expertise.

... the main criticism of the 18-135 is its *edge* sharpness, which has tested to be fairly dismal at certain focal length ranges. If you don't need sharp edges (the posted pic for example) then you should have no problem with this lens.